1. Field of the Disclosure
The present disclosure relates to a magnetic sensor, a method of manufacturing a magnetic sensor, and a method of designing a magnetic sensor.
2. Description of the Related Art
For example, Japanese Unexamined Patent Application Publication No. 2012-119613 discloses a self-pinning type magnetic detection element in which a Pin layer of a GMR film has a Synthetic-Pin structure and a film thickness of a first magnetic layer is made to be appropriate from the viewpoint of heat resistance and ΔMR, and a magnetic sensor using the magnetic detection element. The magnetic sensor has a laminate structure in which a fixed magnetic layer and a free magnetic layer are laminated with a nonmagnetic material layer interposed therebetween, and the fixed magnetic layer is of a self-pinning type in which a first magnetic layer and a second magnetic layer are laminated with a nonmagnetic intermediate layer interposed therebetween and which is magnetized and fixed in antiparallel, the first magnetic layer is formed of FexCo100-x (where x is 55 at % or more and 65 at % or less) which is a material having a higher coercive force than that in the second magnetic layer, the film thickness of the first magnetic layer is in a range of 14 angstroms or more and 20.5 angstroms or less and is thinner than the second magnetic layer, and the difference between the magnetization amounts of the first magnetic layer and the second magnetic layer is substantially zero.
For example, Japanese Unexamined Patent Application Publication No. 2012-185044 discloses a magnetic sensor which can form a plurality of magnetoresistance effect elements, which are different in sensitivity axis direction from each other and configure a bridge circuit, on the same chip, and is excellent in measurement accuracy. In the magnetic sensor, a plurality of magnetoresistance effect elements are provided on the same chip, thereby configuring a bridge circuit. A fixed magnetic layer of each of the magnetoresistance effect elements is of a self-pinned type, and sensitivity axis directions of the magnetoresistance effect elements configuring a series circuit are antiparallel to each other. On the upper surface of a free magnetic layer of each magnetoresistance effect element, an antiferromagnetic layer is provided which can generate a switched connection bias without performing annealing in a magnetic field, between the antiferromagnetic layer and the free magnetic layer, and align a magnetization direction of each free magnetic layer in a direction orthogonal to the sensitivity axis direction in a state where magnetization variation is possible.
In a self-pinning type magnetic detection element, pinning of a fixed magnetic layer is designed so as to be maintained by a coercive force of a ferromagnetic body through an antiferromagnetic body or an antiparallel coupling layer and stably maintain magnetism without being affected by an external magnetic field at room temperature. However, in a high-temperature environment close to a blocking temperature of the antiferromagnetic body or a Curie temperature of the ferromagnetic body, the magnetic field of the fixed magnetic layer rotates due to an external magnetic field, and if a temperature is lowered in that state, magnetization is fixed in a direction different from the direction intended in a design. The fixing of magnetization in an unintended direction causes an error of a sensor, and therefore, it is necessary to suppress this. Therefore, a balance pin design is adopted which makes magnetization amounts of ferromagnetic body layers which are located above and below an antiparallel coupling layer be the same such that a magnetic field does not rotate even if external magnetic field is applied in a high-temperature environment.
However, the magnetization amount of the ferromagnetic body layer depends on a thickness, and it is not possible to make variation in thickness zero due to tolerance in a process of manufacturing the ferromagnetic body layer. Imbalance occurs in the magnetization amount of the ferromagnetic body layer due to variation in thickness, and thus there is a possibility that the magnetization direction of the fixed magnetic layer may change due to an external magnetic field. According to the study of the inventors, it is found that in a case where tolerance of the thickness of the ferromagnetic body layer is set to be ±0.2 angstroms and a direct-current magnetic field of 600 Oe is applied for 1000 hours at a temperature of 150° C., an angle error of about ±0.15 Deg occurs.
These and other drawbacks exist.